iPS cells are also referred to as artificial pluripotent stem cells or induced pluripotent stem cells, which are cells achieving pluripotent differentiation ability equivalent to that of embryonic stem (ES) cells.
Cells having pluripotent differentiation ability, such as ES cells and iPS cells, have the ability to differentiate into all organs and tissues constituting an organism. Accordingly, these cells are expected, to be a highly effective means for reproducing organs, blood, bone marrow, tissue, etc., that are damaged by some diseases.
However, blood, bone marrow, tissue, organs, and other biological materials obtained from ES cells may cause transplant rejection. It is essential to solve such immunological problems, and there are also ethical problems. Conversely, iPS cells can be produced using a patient's own somatic cells; hence, there are neither immunological rejection problems nor ethical problems.
Professor Shinya Yamanaka and his group have succeeded in producing iPS cells by introducing genes of four types of reprogramming factors Oct3/4, Sox2, Klf4, and c-Myc (so-called Yamanaka factors) into mouse fibroblasts (NPL 1 and NPL 2); however, clinical application of the iPS cells has the following problems:
1. There is a possibility that foreign genes, such as bacteria DNA, may be integrated into the genome of the host cell.
2. iPS cells produced by conventional methods have safety problems because they become cancerous at a constant frequency.
3. iPS cells produced by overexpression of foreign genes have unexpected influences, other than pluripotency.